Japanese Examined Patent Publication No. 17,030/1982 discloses a pressure sensitive adhesive tape containing glass microbubbles. Japanese Unexamined Patent Publication No. 217,092/1989 discloses a foamed pressure sensitive adhesive tape containing pigment-coated microbubbles. Japanese Unexamined Patent Publication No. 18,485/1990 discloses an ultraviolet light polymerized acrylic pressure sensitive adhesive agent. U.S. Pat. No. 4,181,752 discloses a method for the formation of a sheet by interposing a liquid polymerizable substance between solid sheet materials and exposing the liquid polymerizable substance, to radiation, thereby polymerizing the substance.
The products of these inventions are characterized by enabling adhesive tapes to achieve an increase in wall thickness, acquire the ability to absorb a shock, enjoy light weight, exhibit strong adhesive force, ensure usability even on an irregular surface, and be produced by photopolymerization. They nevertheless are disadvantageous in that they exhibit little adhesiveness to silicone materials due to the use of an acrylic adhesive agent, show poor susceptibility to perforation, and exhibit low dimensional stability.
Moreover, U.S. Pat. No. 4,839,206 discloses a pressure sensitive adhesive tape wherein one or both of the sides of a foam substrate is laminated with a pressure sensitive adhesive not containing a filler, but this tape does not have a material providing a mechanical reinforcing effect. Therefore, similar to the above-mentioned adhesive tape, it has the drawbacks of poor susceptibility to perforation, low hardness, poor dimensional stability, etc.
Heretofore, a foamed double-faced pressure sensitive adhesive tape has been produced by a method which comprises interposing an acrylic foam substrate monomer or oligomer in the form of a layer between two transparent release sheets, exposing the monomer or oligomer layer to an ultraviolet light, thereby polymerizing the monomer or oligomer and giving rise to an acrylic foam substrate, then peeling one of the transparent release sheets, and attaching fast a laminate formed of a product release sheet and an acrylic pressure sensitive adhesive.
The other surface of the acrylic foam substrate is subjected to the same treatment as described above, resulting in a multilayer pressure sensitive adhesive sheet having acrylic type pressure sensitive adhesive layers formed one each on the opposite surfaces of the acrylic foam substrate and product release sheets attached further to the outer sides of the pressure sensitive adhesive layers. The multilayer pressure sensitive adhesive sheet, optionally, is wound up in a roll after one of the product parting sheets has been separated. At the time that this roll is put to use, the remaining product release sheet is peeled off.
For the multilayer pressure sensitive adhesive tape possessing a foamed substrate, the acrylic foam substrate is used most desirably as the foamed substrate from the practical point of view. When the multilayer pressure sensitive adhesive tape is to be produced by the aforementioned method using this acrylic foam substrate, lamination of a silicone type pressure sensitive adhesive is attained only with difficulty. The reason for this difficulty is that when the silicone type adhesive agent is applied to the acrylic foam substrate in accordance with the method described above, the silicone type adhesive agent exhibits inferior adhesivity to the acrylic foam substrate and tends to separate as attached fast to the release sheet. There further exist such disadvantages as inferior dimensional stability of the adhesive agent, poor susceptibility to perforation, and absence of hardness.
Therefore, an object of the invention is to provide a multilayer pressure sensitive adhesive agent which is free from the various drawbacks possessed by the conventional multilayer pressure sensitive adhesive agent as described above.